So as to reduce fuel consumption and the pollution emitted by motor vehicles, major attempts have been made by tire designers to obtain tires having all of the following: very low rolling resistance, improved adhesion both on dry ground and on wet or snow-covered ground, and very good wear resistance.
Numerous solutions have thus been proposed to lower the rolling resistance and to improve the adhesion of tires, but these generally result in a very great decline in the wear resistance. In particular, it is well known that although the incorporation of conventional white fillers such as, for example, conventional silicas or aluminas, chalk, talc, clays such as bentonite or kaolin, in rubber compositions used for the manufacture of tires and in particular of treads, does result in a reduction in the rolling resistance and an improvement in adhesion to wet, snow-covered or icy ground, it also results in an unacceptable decline in the wear resistance, linked to the fact that these conventional white fillers do not have a sufficient reinforcement ability with respect to such rubber compositions. For this reason, these white fillers are generally referred to as non-reinforcing fillers, also referred to as inert fillers.
One effective solution to this problem has been described in particular in patent applications EP-A-0 501 227, EP-A-0 735 088 or WO99/02602, which disclose diene rubber compositions reinforced with precipitated silicas of high dispersibility (so-called “HD” silicas, for “highly dispersible silica”), which make it possible to manufacture treads having a significantly improved rolling resistance, without adversely affecting the other properties, in particular those of grip, endurance and in particular wear resistance. Other compositions having such a compromise of contradictory properties are also described in applications EP-A-0 810 258 and WO99/02602, with specific aluminous fillers of high dispersibility as reinforcing white fillers.
However, the rubber compositions that contain these specific white fillers, even when they are of the highly dispersible type, remain more difficult to work (“processability”) than rubber compositions filled conventionally with carbon black, because for reasons of mutual attraction, these white filler particles have an irritating tendency to agglomerate together within the elastomeric matrix. These interactions tend to increase the consistency of the compositions in the uncured state and therefore to make them more difficult to work than in the presence of carbon black; they also have the consequence of limiting the dispersion of the filler and hence the reinforcing properties to a substantially lower level than that which it would be theoretically possible to achieve if all the (white filler/elastomer) bonds that could be created during the thermomechanical kneading operations were in fact obtained.
Furthermore, these inorganic fillers of the siliceous or aluminous type also have the known drawback of significantly disrupting the vulcanization kinetics of the elastomeric compositions, compared with conventional compositions filled with carbon black. In particular, in the case of silicas, it is known that the resulting longer curing times may adversely affect the industrial processing of the elastomeric compositions, like that of the rubber articles containing them.